Increasing the safety of currently used fuel tanks, involves the prevention or minimization of fuel vapour leaks. Both the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB), specify the requirement of On-Board Diagnostic II (OBD II) for the check for evaporative emission system for leaks. This requires detecting system leaks equivalent to an orifice larger than 0.5 mm (0.020 inch) in diameter for vehicles produced starting model year 2000.
A fuel tank generally contains fuel in gaseous and liquid form. In particular conditions, e.g. raise of temperature, a dangerous build-up of pressure may occur inside the fuel tank. For that reason it is advantageous to vent the fuel tank, providing there is no emission of hydrocarbons to the atmosphere.
In order to prevent this emission, the fuel tank is generally vented using an evaporative emission control system comprising in general a vapour canister containing an adsorptive material (e.g. charcoal), through which fuel vapours escaping from the fuel tank are directed.
Leaks in the fuel tank or at the interface between the fuel tank and components (e.g. canister, valves, . . . ) may exist and their presence must be checked.